Application layer firewall on FreeBSD, is it possible ?

Robert Watson rwatson at
Wed Aug 31 11:19:10 GMT 2005

On Tue, 30 Aug 2005, [iso-8859-2] Daniel Dvo?ák wrote:

> So, is there any way to do same application layer osi model firewall 
> with FreeBSD gateway ?
> Of course, I tried to find on web, I have not been successful in 
> searching so far.
> If my question is not right in this mailing list, if my question is 
> annoying here, so I am sorry.

I can't speak to the details of the environment or protocols, but you 
might take a look at "ipfw fwd", which allows you to locally intercept 
wide area network TCP connections passing through an IP router.  This can 
be used for things like transparent proxy caching, transparent firewalls, 
and so on.  ipfw(8) contains some details, but I've not played with it 
myself so I can't tell you much more than that it looks like applications 
can simply bind a TCP port, and then you can use ipfw fwd to redirect 
connections to it.  I'm not sure how well ICMP is handled.

Robert N M Watson

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